3Rs of drought: resistance, resilience and recovery - an opportunistic experiment

2022年夏天，英格兰出现了有记录以来最高的气温和自1935年以来最低的7月降雨量。这场欧洲500年来最严重的干旱导致英格兰和威尔士大部分地区的河道普遍干涸。虽然干旱在历史上是极端的，但它提供了气候变化预期条件的预感：这种极端的水文气候事件预计将在未来变得更加频繁。我们预测干旱对生活在河流中的生物群落的影响，从而减轻最严重的影响的能力，受到对影响其抵抗干旱影响和一旦恢复洪水后恢复能力的因素的有限了解的限制。这里河床的底物尤其重要，因为一旦失去地表水，许多动物就会退回到潮湿的地下底物中。如果不清楚底物特性如何影响河流对干旱的反应，河流管理者就无法优先保护最脆弱的河流免受干旱。我们处于一个独特的位置，已经在多个重复的河道中进行了一项实验，这将使我们能够通过实验研究底质/细沉积物对河流群落对干旱的反应的影响，以及它们在恢复水流后重新定居和恢复的潜力。这项实验旨在观察底物组成和细微沉积物负荷对大型无脊椎动物群落的影响，这些群落在干旱期间水位下降时自然干燥，处理留在原地。我们将探索底物特性如何影响i)无脊椎动物在河床上坚持干旱的能力，ii)一旦恢复水流，无脊椎动物通过从河床出来重新殖民河流的能力，以及iii)与其他殖民路线(空中或漂流)相比，从河床重新殖民的相对重要性。

The summer of 2022 has seen the highest air temperatures ever recorded in England and the lowest July rainfall since 1935. This drought, the worst in Europe for 500 years, has resulted in the widespread drying of river channels over large parts of England and Wales. Whilst extreme in historic terms, the drought provides a foretaste of the conditions expected with climate change: such extreme hydroclimatic events are expected to become more frequent in the future. Our ability to predict the impact of such droughts on the biological communities living in rivers, and hence mitigate the most severe effects, is constrained by a limited understanding of the factors influencing their abilities to resist the effects of drought and to recovery once flow resumes. Here the substrate of the river bed is particularly important, as many animals will retreat into wet subsurface substrate once surface water has been lost. Without a clear understanding of how substrate characteristics affect the response of rivers to drought, river managers cannot prioritize the most vulnerable rivers for protection from drying. We are in a unique position of having an experiment already set up in multiple replicated stream channels that will enable us to experimentally examine the effects of substrate/fine sediment on the response of river communities to drought and on their potential to recolonise and recover following the resumption of flow. The experiment, set up to look at the effects of substrate composition and fine sediment loading on the macroinvertebrate communities dried naturally as water levels declined during the drought, with the treatments left in situ. We will explore how substrate characteristics influence i) the ability of invertebrates to persist through drought in the river bed, ii) the ability of invertebrates to recolonise the river by emerging from the river bed once flow resumes, and iii) the relative importance of recolonisation from the river bed compared with other routes of colonization (aerial or drifting).